1. Field of the Invention
The present invention relates to the filed of automated measurement systems for use in analysis and in in-vitro diagnosis. In particular, the apparatus described enables automatic quality control and validation of characteristic process engineering parameters, in particular characteristic optical parameters, during the measurement of scattered light signals.
2. Description of the Related Art
An increasing demand for sensitive optical detection methods which can be used in fully automated analyzers appertaining to laboratory diagnosis has evolved in recent years.
In addition to the requirements made of the measurement method, such as sensitivity, resolution or dynamic range, the high degree of automation means that, in the same way, requirements are also made of the automated testing, setting and, if appropriate, readjustment of the parameters of the measurement method used. Therefore, quality control and validation measures must likewise be ensured by automated methods.
In the different methods of analysis, the testing and securing of valid results are characterized by varying degrees of difficulty. While testing is possible in absorption spectroscopy, for example by using officially calibrated standards, this is not possible for methods of scattered light spectroscopy. In the method of forward light scattering, in particular, which utilizes angles or angular ranges near the incident beam of the light source, simultaneous measurement of characteristic optical parameters within the beam path is difficult on account of the mechanical structure. Therefore, characteristic optical parameters, such as intensity, wavelength, pulse length or noise component of the light source used, and with the use of a vessel (cuvette or the like) which serves to accommodate the material to be measured and is briefly inserted into the beam path, can frequently be determined only with the aid of an additional relative standard. However, the necessity of using nonstandardized test media gives rise to further fault sources which do not allow control over a relatively long period of time in situ and do not allow an unambiguous conclusion to be drawn about the property of the instrumental conditions.
In scattered light apparatuses, high-purity solutions 5 such as toluene, for example, are used in the majority of cases for reference measurements. Measurement of the angle-dependent scattered light characteristic produces a profile and thus a measure of quality for the apparatus used.
The use of such liquids is problematic for reasons of safety and, in addition, carrying out the measurements described above is time-intensive and complicated in terms of laboratory technology. For these reasons, these methods cannot be used for application in automated analyzers. However, if a corresponding material to be measured which generates scattered light is not present, no measurement signal can be generated and thus no conclusion can be drawn about the quality of the method under the current operating conditions.
Consequently, if a material to be measured which generates scattered light is used, then it will generate a signal which differs from measurement to measurement, depending on its composition, its structure and the procedure for its use. Simultaneous validation of the measurement system is thus precluded. These considerations also apply in a similar manner to methods in which the measurement signals are generated initially within the material to be measured, such as, for example, in the case of fluorescence or chemiluminescence reactions.
In the arrangement used most for scattered light measurement, the scattered light is detected under an angular range around 90° with respect to the direction of the incident beam. Separation of the incident light from the scattered light is particularly easy to achieve as a result. Alternatively, choosing a larger solid-angle range and utilizing angles or angular ranges around the forward direction of the incident light make it possible to achieve higher intensities of the scattered light, as a result of which an arrangement can be constructed in a technically simpler and more cost-effective manner. The proportion of scattered light at angles around the forward direction is particularly high precisely for the measurements (which are striven for in accordance with the present description) on organic macromolecules for use in human in-vitro diagnosis. In addition, use is made of the effect of increasing the intensity of the scattered light by the principle of particle enhancement. The dependence of the scatter signal on the particle size is the most favorable for the case in which the scattering particles are of an order of magnitude which corresponds to the order of magnitude of the wavelength of the incident light. This produces a preferred arrangement which makes it possible to utilize these components for the measurement. Fundamental considerations and calculations concerning the theory of scattered light are contained in the appropriate textbooks. The following may be mentioned here by way of example: H. C. van de Hulst (Light Scattering by Small Particles, Dover Publications, Inc. New York, 1957, 1981) and C. F. Bohren, D. R. Huffman (Absorption and Scattering of Light by Small Particles, J. Wiley & Sons, New York, 1983). Given further knowledge of the properties of the material to be measured which is to be examined, discrimination of the material to be measured into magnitude classes can be achieved by selection of one or more angular ranges.
The apparatuses used in automated laboratory diagnosis are frequently constructed from, these being known per se to a person skilled in the art, movable units (e.g. rack, carousel, rotor or the like) for accommodating a multiplicity of vessels for sample or reagent liquids and the vessels for accommodating and passing through the material to be measured (cuvettes). In the event of using a rotatable unit for the positioning of the material to be measured, the cuvettes, in dependence on their requirements imposed on the measurement recording, are guided cyclically past a stationary position of the measurement unit. When scattered light measurements are carried out, the resultant scattered light is produced by the material to be measured in a cuvette, said material being introduced into the beam path. This means that changes can be produced by different positioning of the material to be measured.